A mother convicted of beating her two-year-old son to death after subjecting him to months of horrific cruelty has been jailed for life.

Rebecca Shuttleworth was ordered to serve at least 18 years in jail after being convicted on Monday of murdering Keanu Williams following a six-month trial.

Shuttleworth, who was sentenced by Mr Justice Spencer at Birmingham Crown Court, had also been found guilty of four counts of child cruelty. The 25-year-old inflicted what detectives described as "horrifying" injuries on Keanu after apparently convincing her support worker that she had turned her life around.

It emerged on Tuesday that Shuttleworth was filmed celebrating a £10,000 lottery win while on bail for the murder of Keanu, whose body showed 37 external marks of injury.

A two-minute video posted on YouTube by the People's Postcode Lottery shows the 25-year-old shouting in delight as her friend is presented with a "Street Prize" cheque outside a property in Rusholme, Manchester. Keanu was pronounced dead on January 9 2011 after paramedics were called to his mother's partner's flat in Old Moat Way, Ward End, Birmingham.

The judge, who also passed concurrent sentences for child cruelty totalling four years, told Shuttleworth: "The jury have convicted you of the brutal murder of your two-year-old son. He was a defenceless child and it was your duty to protect him. Instead, you beat him so severely he died a lingering death from his injuries a day or so later."

Paying tribute to Keanu, the judge added: "He was a delightful little boy described as a real character, a little entertainer who remained cheerful despite everything. Joyful was the word that more than one witness used to describe him - he was a favourite at nursery as well as within the family. His death has left a void in many lives which will never be filled."

Shuttleworth's partner, Luke Southerton, was cleared of murder, manslaughter and causing or allowing the death of a child, but convicted of one incident of cruelty towards Keanu during which he was bitten. Southerton, 32, was given a nine-month jail term suspended for two years and ordered to complete 200 hours of unpaid work for the community.

A serious case review into Keanu's death, which is expected to examine social services contact with his mother, will be published in the near future. In a statement issued after Shuttleworth was unanimously convicted, the chairwoman of Birmingham's Safeguarding Children Board acknowledged that chances to take action had been missed.

Jane Held, the independent chairwoman of the multi-agency Board, said: "This is an extremely sad case and my sympathies are with those who knew Keanu. While we can't go into detail prior to the review being made public, it is clear from this trial that professionals in the different agencies involved missed a significant number of opportunities to intervene and take action."